Most central nervous system (CNS) injuries include stroke, trauma, hypoxia-ischemia, multiple sclerosis, seizure, infection, and poisoning directly or indirectly involve a disruption of blood supply to the CNS. These injuries share the same common pathologic process of rapid cerebral edema leading to irreversible brain damage and eventually to brain cell death.
One common injury to the CNS is stroke which is the destruction of brain tissue as a result of intracerebral hemorrhage or ischemia. Stroke may be caused by reduced blood flow or ischemia that results in deficient blood supply and death of tissues in one area of the brain (infarction). The causes of ischemic stroke include blood clots that form in the blood vessels in the brain (thrombus) and blood clots or pieces of atherosclerotic plaque or other material that travel to the brain from another location (emboli). Bleeding (hemorrhage) within the brain may also cause symptoms that mimic stroke.
The CNS tissue is highly dependent on blood supply and is very vulnerable to interruption of blood supply. Without neuroprotection, even a brief interruption of the blood flow to the CNS can cause neurological deficit. The brain is believed to tolerate complete interruption of blood flow for a maximum of about 5 to 10 minutes. It has been observed that after blood flow is restored to areas of the brain that have suffered an ischemic injury, secondary hemodynamic disturbances have long lasting effects that interfere with the ability of the blood to supply oxygen to CNS tissues. Similarly, interruption of the blood flow to the spinal cord, for even short periods of time, can result in paralysis.
Recognition of the “ischemic penumbra,” a region of reduced cerebral blood flow in which cell death might be prevented, has focused attention on treatments that might minimize or reverse brain damage when the treatments are administered soon after stroke onset. To date, several classes of neuroprotective compounds have been investigated for acute stroke. They have included calcium channel antagonists, N-methyl-D-aspartate (NMDA) receptor antagonists, free radical scavengers, anti-intercellular adhesion molecule 1 antibody, GM-1 ganglioside, γ-aminobutyric acid agonists, and sodium channel antagonists, among others. Results from various trials have yielded disappointing efficacy results and some evidence of safety problems, including increased mortality or psychotic effects which resulted in their early termination.
Multiple sclerosis (MS) is another disease of the CNS. MS is an inflammatory demyelinating disease, which typically displays a relapsing-remitting course characterized by episodes of neurological disability followed by periods of partial or complete clinical remission (Lucchinetti et al., 2000, Ann. Neurol. 47:707-717; Hemmer et al., 2002, Nat. Rev. Neurosci. 3:291-301). Most patients later enter a progressive phase of steady decline of neurological function. Severe axonal loss and neuronal death are frequent in MS (Ferguson et al., 1997, Brain 120 (Pt. 3):393-399; Trapp et al., 1998, N. Engl. J. Med 338:278-285; Peterson et al., 2001, Ann. Neurol. 50:389-400; Bjartmar et al., 2003, Neurotox. Res. 5:157-164). Axonal loss is a major cause of permanent neurological deficit in MS (Wujek et al., 2002, J. Neuropathol. Exp. Neurol. 61:23-32; Bjartmar et al., 2003, J Neurol. Sci. 206:165-171; Medana et al., 2003, Brain 126:515-530). Chronically demyelinated axons may degenerate due to a lack of myelin-derived trophic support (Bjartmar et al., 2003, J Neurol. Sci. 206:165-171); however, no current therapies for MS are known provide at axonal protection (Bectold, et al., 2004, Ann. Neurol. 55:607-616).
Cellular therapy serves as an alternative to drug therapy. It has been demonstrated that intracerebral transplantation of donor cells from embryonic tissue may promote neurogenesis (Snyder et al., 1997 Adv Neurol. 72:121-32). Intrastriatal fetal graft has been used to reconstruct damaged basal ganglia circuits and to ameliorate behavioral deficits in a mammalian model of ischemia (Goto et al., 1997 Exp Neurol. 147:503-9). Fetal hematopoietic stem cells (HSCs) transplanted into the adult organism or adult HSCs transplanted into an embryo results in a chimera that reflects the endogenous cells within the microenvironment into which the cells were seeded (Geiger et al., 1998, Immunol Today 19:236-41). Pluripotent stem cells are harbored in the adult CNS and the adult brain can form new neurons (Gage, 1998 Curr. Opin. Neurobiol. 8:671-6; Kempermann and Gage, 1998 Nat Med. 4:555-7).
Bone marrow contains at least two types of stem cells, hematopoietic stem cells and stem cells of non-hematopoietic tissues variously referred to as mesenchymal stem cells or marrow stromal cells (MSCs) or bone marrow stromal cells (BMSCs). These terms are used synonymously throughout herein. MSCs are of interest because they are easily isolated from a small aspirate of bone marrow and they readily generate single-cell derived colonies. The single-cell derived colonies can be expanded through as many as 50 population doublings in about 10 weeks, and can differentiate into osteoblasts, adipocytes, chondrocytes (Friedenstein et al., 1970 Cell Tissue Kinet. 3:393-403; Castro-Malaspina et al., 1980 Blood 56:289-301; Beresford et al., 1992 J. Cell Sci. 102:341-351; Prockop, 1997 Science 276:71-74), myocytes (Wakitani et al., 1995 Muscle Nerve 18:1417-1426), astrocytes, oligodendrocytes, and neurons (Azizi et al., 1998 Proc. Natl. Acad. Sci. USA 95:3908-3913); Kopen et al., 1999 Proc. Natl. Acad. Sci. USA 96:10711-10716; Chopp et al., 2000 Neuroreport II 3001-3005; Woodbury et al., 2000 Neuroscience Res. 61:364-370). For these reasons, MSCs are currently being tested for their potential use in cell and gene therapy of a number of human diseases (Horwitz et al., 1999 Nat. Med. 5:309-313; Caplan, et al. 2000 Clin. Orthoped. 379:567-570).
MSCs constitute an alternative source of pluripotent stem cells. Under physiological conditions they maintain the architecture of bone marrow and regulate hematopoiesis with the help of different cell adhesion molecules and the secretion of cytokines, respectively (Clark and Keating, 1995 Ann NY Acad Sci 770:70-78). MSCs grown out of bone marrow by their selective attachment to tissue culture plastic can be efficiently expanded (Azizi et al., 1998 Proc Natl Acad Sci USA 95:3908-3913; Colter et al., 2000 Proc Natl Acad Sci USA 97:3213-218) and genetically manipulated (Schwarz et al. 1999 Hum Gene Ther 10:2539-2549).
MSC are also referred to as mesenchymal stem cells because they are capable of differentiating into multiple mesodermal tissues, including bone (Beresford et al., 1992 J Cell Sci 102:341-351), cartilage (Lennon et al., 1995 Exp Cell Res 219:211-222), fat (Beresford et al., 1992 J. Cell. Sci. 102:341-351) and muscle (Wakitani et al., 1995 Muscle Nerve 18:1417-1426). In addition, differentiation into neuron-like cells expressing neuronal markers has been reported (Woodbury et al., 2000 J Neurosci Res 61:364-370; Sanchez-Ramos et al., 2000 Exp Neurol 164:247-256; Deng et al., 2001 Biochem Biophys Res Commun 282:148-152), suggesting that MSC may be capable of overcoming germ layer commitment.
The concept of transplantation of bone marrow has been studied by others. For example, in the Azizi et al. reference, the investigators transplanted human bone marrow stromal cells (hBMSCs) into the brains of albino rats (Azizi et al., 1998 Proc Natl Acad Sci USA 95:3908-3913). Their primary observations were that hBMSCs can engraft, migrate and survive in a manner similar to rat astrocytes. Further, it has been demonstrated that the bone marrow cells when implanted into the brain of adult mice can differentiate into microglia and macroglia (Eglitis et al., Proc Natl Acad Sci USA 1997 94:4080-5). Again, this occurred when the bone marrow cells were transplanted into the brain of normal mice. There have been many attempts made to use bone marrow stromal cells in cell therapy in an animal model. However, there has been little evidence of using bone marrow stromal cells in a diseased animal model or otherwise an animal that is suffering from a disease. Thus, there is a long felt need in the art for efficient and directed means of treating a neurodegenerative disease such as MS in a mammal. The present invention satisfies this need.